linux-kernel - Re: [PATCH 4/9v2] usb: host: ehci.h: fix single statement macros

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Date:	Thu, 10 Dec 2015 15:04:07 -0300
From:	"Geyslan G. Bem" <geyslan@...il.com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:	Peter Senna Tschudin <peter.senna@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-usb@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/9v2] usb: host: ehci.h: fix single statement macros

2015-12-10 14:47 GMT-03:00 Sergei Shtylyov <sergei.shtylyov@...entembedded.com>:
> On 12/10/2015 08:40 PM, Geyslan G. Bem wrote:
>
>>>>>>>>> Don't use the 'do {} while (0)' wrapper in a single statement
>>>>>>>>> macro.
>>>>>>>>>
>>>>>>>>> Caught by checkpatch: "WARNING: Single statement macros should not
>>>>>>>>> use a do {} while (0) loop"
>>>>>>>>>
>>>>>>>>> Signed-off-by: Geyslan G. Bem <geyslan@...il.com>
>>>>>>>>> ---
>>>>>>>>>      drivers/usb/host/ehci.h | 4 ++--
>>>>>>>>>      1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
>>>>>>>>> index cfeebd8..945000a 100644
>>>>>>>>> --- a/drivers/usb/host/ehci.h
>>>>>>>>> +++ b/drivers/usb/host/ehci.h
>>>>>>>>> @@ -244,9 +244,9 @@ struct ehci_hcd {                   /* one per
>>>>>>>>> controller */
>>>>>>>>>            /* irq statistics */
>>>>>>>>>      #ifdef EHCI_STATS
>>>>>>>>>            struct ehci_stats       stats;
>>>>>>>>> -#      define COUNT(x) do { (x)++; } while (0)
>>>>>>>>> +#      define COUNT(x) ((x)++)
>>>>>>>>>      #else
>>>>>>>>> -#      define COUNT(x) do {} while (0)
>>>>>>>>> +#      define COUNT(x) ((void) 0)
>>>>>>>>
>>>>>>>>
>>>>>>>>       Why not just empty #define?
>>>>>>>
>>>>>>>
>>>>>>> Indeed. I'll change it.
>>>>>>> Tks Sergei.
>>>>>>
>>>>>>
>>>>>> Since COUNT is not used to return the empty #define is ok. Another way
>>>>>> is to use #define COUNT(x) (0) to get a 0 when necessary to read
>>>>>> returns.
>>>
>>>
>>>>>      Just 0, no parens please.
>>>
>>>
>>>> Ok, no parens, since there's no evaluation.
>>>
>>>
>>>     It's because the literals don't need parens at all.
>>>
>>>> Then my change is:
>>>>
>>>> -#      define COUNT(x) do { (x)++; } while (0)
>>>> +#      define COUNT(x) (++(x))
>>>>    #else
>>>> -#      define COUNT(x) do {} while (0)
>>>> +#      define COUNT(x) 0
>>>>
>>>> Pre-increment allowing to return the updated x.
>>>
>>>
>>>
>>>     Why if there was a post-increment before?
>
>
>> There's nothing wrong with post-increment. The pre one would be
>> necessary if using return.
>
>
>    Maybe it was intended to return the old value? :-)
>
>>>
>>>     Anyway, this talk is quite pointless since the macro didn't return
>>> any
>>> value anyway.
>>
>> You're sure, there's no use anywhere of the return of that macro indeed.
>
>
>    *do* {} *while* (0) just couldn't return any value, it's not just a
> compound statement which gcc indeed allows to be evaluated.
Indeed. :-)

v2 in the oven.
>
>
>> Sending v2 soon.
>
>
> MBR, Sergei
>



-- 
Regards,

Geyslan G. Bem
hackingbits.com
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